The present invention generally relates to machine tools, and more particularly relates to laser equipped CNC machine tools having long laser beam paths and that are used to cut and weld parts from carbon steels, stainless steel and aluminum.
Flying optic and cantilever type CNC laser cutting and welding machines with cutting areas of two meters by 4 meters and above have long beam paths, the distance between the laser and the focal optic, exceeding 8 meters in length. Individual sections of the beam path can exceed 6 meters in length. Such machines also may have an optical carriage having a short wheelbase, the distance between linear bearings on a common linear way. For example, an optical carriage may be used for the purpose of maintaining a constant length beam path, as opposed to a variable length beam path between the laser and the cutting nozzle.
When a short wheelbase exists, small deviations in flatness of machine mounting elements and/or of the linear way raceways cause angular deviation in pointing of a laser beam by slightly pitching, yawing, or rolling the carried reflecting mirror as the optical carriage traverses the linear ways from end to end. Small angular deviations are magnified by a long beam path length (deviation=distance between reflecting mirror and the next impinging mirror times the tangent of the change in reflection angle) and can be a source of significant error when a laser beam impinges on a mirror or a lens several meters from the reflecting mirror. Such errors cause the laser beam to impinge on and be reflected from a different position on the mirror than intended. As a result, further along the laser beam path, a focused beam will shift from its centered position within a cutting nozzle or a welding head thus causing degradation of cutting quality, of part accuracy, of weld position or weld quality.
Optical cube corner retroreflectors have a characteristic that any radiation ray entering its end face will be totally internally reflected and will emerge from the end face parallel to itself, but with the opposite direction of propagation. This property is, within acceptable angle ranges, independent of the precise orientation of the retroreflector. Many examples have been found of cube corner retroreflectors used internally to a laser resonator for some purpose. No example has been found of a cube corner retroreflector used to improve pointing stability of a laser beam in a beam path external to a laser resonator.
It is an objective of the invention to provide a cube corner laser beam retroreflector apparatus that will reduce the effect of small deviations in flatness of optical carriage mounting elements and/or linear ways that pitch, yaw and roll the carried retroreflector apparatus. Inventor testing of such an apparatus reveals significant improvement in the pointing stability of a laser beam reflected by the apparatus. Small changes in pitch, yaw and roll are converted to a small translation in position of the beam reflected from the apparatus. However, since the reflected beam remains parallel to the incoming beam, the length of the beam path does not magnify such small deviations in position and system pointing stability is greatly improved.
It is another objective of the invention to provide a cube corner device, for a beam path external to a laser, which is composed of three orthogonal removable mirrors.
It is a further objective of the invention to provide a laser beam retroreflector apparatus consisting of three adjustable mirrors that are preset to orthogonal relationship to each other before introduction into a beam path.
It is another objective of the invention to provide a cube corner device mirror holding frame, for a beam path external to a laser, which can be fabricated of laser cut tabbed and slotted parts that are welded together.